1. Field of the Invention
The present invention generally relates to a video cadence detecting technique, and more particularly, to a flexible video cadence detecting technique.
2. Description of Related Art
The shooting speed of a film is usually different from the play speed thereof. The film shooting speed may be 24 Hz, while the general play speed may be 60 Hz in the NTSC standard and 50 Hz in the PAL&SECAM standard. Thus, a film is pulled down to the desired play standard in order to be played in the NTSC standard or the PAL&SECAM standard.
For example, when the play speed of a film is to be changed from 24 Hz to 50 Hz in the PAL standard, each image is split into an even image and an odd image. As generally known, an even image is composed of pixels taken from even-numbered scan lines in an original image, and an odd image is composed of pixels taken from odd-numbered scan lines in an original image. By splitting an image into an even image and an odd image, the play speed can be changed from 24 Hz into about 50 Hz. In other words, original images are split according to the speed required by the play standard and a selected video cadence and played in an interlaced manner.
Contrarily, if field images are to be restored into original images, the video cadence of the field images needs to be detected so that the field images can be restored into the original images according to the video cadence.
FIG. 1 is a system block diagram illustrating how conventionally field images are restored into an original film. Referring to FIG. 1, the motion detecting unit 100 determines whether or not there is motion in a current field image by referring to a previous field image and a next field image. For example, if the current field image and the next field image are respectively an even image and an odd image from the same original image, the motion detecting unit 100 determines that there is no motion in the current field image. If the current field image and the next field image are respectively an even image and an odd image from different original images, the motion detecting unit 100 determines that there is no motion in the current field image. In other words, whether or not there is motion in each field image is determined to obtain a pattern.
The cadence pattern recognizing unit 102 compares the pattern detected by the motion detecting unit 100 with data in the cadence database 104 to obtain a corresponding cadence pattern. Finally, the de-interlacing unit 106 restores each original image (also referred as a frame) according to the cadence pattern.
In the conventional technique described above, the cadence database 104 is disposed for storing different cadence patterns, so as to correctly restore field images into an original film. Besides, the system cannot work properly if more cadence patterns are used and these cadence patterns are not stored in the cadence database 104.